Quantum black holes from null expansion operators

Using a recently developed quantization of spherically symmetric gravity coupled to a scalar field, we give a construction of null expansion operators that allow a definition of general, fully dynamical quantum black holes. These operators capture the intuitive idea that classical black holes are defined by the presence of trapped surfaces, that is surfaces from which light cannot escape outward. They thus provide a mechanism for classifying quantum states of the system into those that describe quantum black holes and those that do not. We find that quantum horizons fluctuate, confirming long-held heuristic expectations. We also give explicit examples of quantum black hole states. The work sets a framework for addressing the puzzles of black hole physics in a fully quantized dynamical setting.Comment: 5 pages, version to appear in CQ

Flat slice Hamiltonian formalism for dynamical black holes

We give a Hamiltonian analysis of the asymptotically flat spherically symmetric system of gravity coupled to a scalar field. This 1+1 dimensional field theory may be viewed as the "standard model" for studying black hole physics. Our analysis is adapted to the flat slice Painleve-Gullstrand coordinates. We give a Hamiltonian action principle for this system, which yields an asymptotic mass formula. We then perform a time gauge fixing that gives a Hamiltonian as the integral of a local density. The Hamiltonian takes a relatively simple form compared to earlier work in Schwarzschild gauge, and therefore provides a setting amenable to full quantisation.Comment: 11 pages, refererences added, discussions clarified, version to appear in PR

Spin-Injection Spectroscopy of a Spin-Orbit Coupled Fermi Gas

The coupling of the spin of electrons to their motional state lies at the heart of recently discovered topological phases of matter. Here we create and detect spin-orbit coupling in an atomic Fermi gas, a highly controllable form of quantum degenerate matter. We reveal the spin-orbit gap via spin-injection spectroscopy, which characterizes the energy-momentum dispersion and spin composition of the quantum states. For energies within the spin-orbit gap, the system acts as a spin diode. To fully inhibit transport, we open an additional spin gap, thereby creating a spin-orbit coupled lattice whose spinful band structure we probe. In the presence of s-wave interactions, such systems should display induced p-wave pairing, topological superfluidity, and Majorana edge states

Even-denominator Fractional Quantum Hall Effect at a Landau Level Crossing

The fractional quantum Hall effect (FQHE), observed in two-dimensional (2D) charged particles at high magnetic fields, is one of the most fascinating, macroscopic manifestations of a many-body state stabilized by the strong Coulomb interaction. It occurs when the filling factor ($\nu$) of the quantized Landau levels (LLs) is a fraction which, with very few exceptions, has an odd denominator. In 2D systems with additional degrees of freedom it is possible to cause a crossing of the LLs at the Fermi level. At and near these crossings, the FQHE states are often weakened or destroyed. Here we report the observation of an unusual crossing of the two \emph{lowest-energy} LLs in high-mobility GaAs 2D $hole$ systems which brings to life a new \emph{even-denominator} FQHE at $\nu=1/2$

Neurological disorders in rural Africa - a systematic approach

Leishmaniasis in Northern and Western Africa: A Review Background/Objectives Empirical knowledge suggests that neurological disorders are common in sub-Saharan Africa. However, to date prevalence studies are scarce. The aims of our study were to assess the hospital-based prevalence of neurological disorders in a rural African setting and to describe the pattern of disease by using a systematic approach. Methods The study was conducted at the Haydom Lutheran Hospital in northern Tanzania, Manyara region. Over a period of eight months all patients admitted to hospital were seen prospectively in consecutive order by aneurologist (ASW). Results Out of 8676 admissions 740 patients (8.5%) were given a neurological diagnosis. The most frequent neurological disorders were seizures (26.6%) and infectious diseases (18.1%). The overall mortality of neurological disease was 21%. Cases were grouped according to diagnostic certainty. We suggest three major categories for neurological disorders (group 1 = no diagnostic uncertainties; group 2 = minor diagnostic uncertainties; group 3 = major diagnostic uncertainties) with implications regarding therapy and prognosis. Conclusions The above data emphasizes that neurological disease contributes substantially to morbidity and mortality in a rural African hospital. Based on the observed pattern of neurological disorders we suggest a systematic approac

Real space first-principles derived semiempirical pseudopotentials applied to tunneling magnetoresistance

In this letter we present a real space density functional theory (DFT) localized basis set semi-empirical pseudopotential (SEP) approach. The method is applied to iron and magnesium oxide, where bulk SEP and local spin density approximation (LSDA) band structure calculations are shown to agree within approximately 0.1 eV. Subsequently we investigate the qualitative transferability of bulk derived SEPs to Fe/MgO/Fe tunnel junctions. We find that the SEP method is particularly well suited to address the tight binding transferability problem because the transferability error at the interface can be characterized not only in orbital space (via the interface local density of states) but also in real space (via the system potential). To achieve a quantitative parameterization, we introduce the notion of ghost semi-empirical pseudopotentials extracted from the first-principles calculated Fe/MgO bonding interface. Such interface corrections are shown to be particularly necessary for barrier widths in the range of 1 nm, where interface states on opposite sides of the barrier couple effectively and play a important role in the transmission characteristics. In general the results underscore the need for separate tight binding interface and bulk parameter sets when modeling conduction through thin heterojunctions on the nanoscale.Comment: Submitted to Journal of Applied Physic

Far-flung Filaments of Ejecta in the Young Supernova Remnant G292.0+1.8

New optical images of the young SNR G292.0+1.8, obtained from the 0.9-m telescope at CTIO, show a more extensive network of filaments than had been known previously. Filaments emitting in [O III] are distributed throughout much of the 8 arcmin diameter shell seen in X-ray and radio images, including a few at the very outermost shell limits. We have also detected four small complexes of filaments that show [S II] emission along with [OIII]. In a single long-slit spectrum we find variations of almost an order of magnitude in the relative strengths of oxygen and sulfur lines, which must result from abundance variations. None of the filaments, with or without [S II], shows any evidence for hydrogen, so all appear to be fragments of pure SN ejecta. The [S II] filaments provide the first evidence for undiluted products of oxygen burning in the ejecta from the supernova that gave rise to G292.0+1.8. Some oxygen burning must have occurred, but the paucity of [S II]-emitting filaments suggests that either the oxygen burning was not extensive or that most of its products have yet to be excited. Most of the outer filaments exhibit radial, pencil-like morphologies that suggest an origin as Rayleigh-Taylor fingers of ejecta, perhaps formed during the explosion. Simulations of core-collapse supernovae predict such fingers, but these have never before been so clearly observed in a young SNR. The total flux from the SNR in [OIII] 5007 is 5.4 * 10**-12 ergs/cm**2/s. Using a distance of 6 kpc and an extinction correction corresponding to E(B-V) = 0.6 (lower than previous values but more consistent both with our data and radio and X-ray estimates of NH), this leads to a luminosity of 1.6 * 10**35 ergs/s in the 5007 Ang. line.Comment: 32 pages including 10 figures, and 3 tables, accepted for publication in AJ. Vol 132, July 2006. Higher resolution versions of the figures and a pdf of the manuscript can be found at http://www-int.stsci.edu/~long/papers/g292_optical